Building up of highly sensitive cascade amplifiers



Deg. 27, 1938.

Y K. SCHLESINGER BUILDING UP 0F HIGHLY SENSITIVE oAscAbE AMPLIFIERS Filed June '7, 1935 3 Sheets-Sheet l I Jm ea/ o/I M 9/1.

Dec. 27, 1938. K SCHLESINGER 2,141,413

BUILDING UP 0F HIGHLY SENSITIVE CASCADE AMPLIFIERS Fild June 7, 1955 :s Sheets-Sheet 2 Z yen/0'47 Dec. 27, 1938. K. SCHLESINGER I BUILDING UP OF HIGHLY SENSITIVE CASCADE AMPLIFIERS Filed June 7, 1935 3 Sheets-Sheet 3 mm w 325 vs vim 2.: r

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UNITED. STATES PATENT OFFICE BUILDING UP OF HIGHLY SENSITIVE CASCADE AMPLIFIERS Kurt Schlesinger, Berlin, Germany, assignor to Radioakticngesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application June 7, 1935, Serial No. 25,415 V In Germany June 9, 1934 '7 Claims. (01. 250-27) In an amplifier arrangement with a plurality Fig. l shows'the circuit of a portion of an of amplifying tubes, in which all tubes amplify intermediate frequency amplifier of a superthe same frequency band, for instance the interheterodyne receiver,

mediate frequency of a superheterodyne receiver, Fig. 2 shows the construction of a coupling 5 difficulties arise, as well known, by reason of device, 5 undesirable reaction couplings. In addition to Fig. 3 shows the construction of another couthese known effects there appears a new group of pling device and disturbances if the amplifying tubes employed Fig. 3a shows the circuit of the mixing tube have a particularly large effective steepness which precedes the intermediate frequency amplifier of Fig. 1. 10'

(8:5 Ina/Volt) Fig. 4 shows the method of connecting together In modern television art it is possible, on acthe heating leads of the oscillating and amplifycount of the absence of strong disturbance in ing stages in a superheterodyne' circuit.

the ultra-short wave band, to employ inter- In Fig. 1 there is illustrated a group of two if: mediate frequency mp fi rs v n a total amplifying tubes l and 2, such as are used in amplification amounting to about ten times that the intermediate frequency amplifier of a telepossible in the case of sound reception on the vision superheterodyne, and of which each single medium wave band. It is necessary for the valves tube is furnished with a steepness of approxiin such intermediate frequency amplifiers to have mately 6 milliamperes per volt, or more, and

very large slopes, as the effective anode resistpermits ofan amplification of approximately 20 ances in the case of television are very much per stage. For each stage filters are arranged in smaller than the resonance circuit resistances in the anode circuit, screen-grid circuit and controlthe radio art (order of magnitude 5,000 ohms as grid circuit consisting of filter resistance in these compared with several hundred thousand ohms). leadings andby-passing decoupling condensers.

25 Finally, with the object of preventing potential- It has been found that the decoupling con- 25 overloading of the control grid of the television densers, which in Fig. 1 are designated 3, i and 5 tube with its very harmful effects on the quality for the control grid circuit, anode circuit and of the image, and also an inadmissibly high screening-grid circuit should not be connected in amplification of the humming in the mains, a the well known manner with the metallic receiver low-frequency amplification after the interchassis 6, the earth or mass, but inaccordance mediate frequency rectifier is preferably diswith the invention may be connected directly with pensed with entirely. The intermediate frethe cathode of each corresponding stage. It'is quency amplifier alone must accordingly cope convenient and advantageous tocombine thewith the whole reception amplification, and three or more blocking condensers aforesaid to possess a degree of amplification which is greater form a common combination condenser, which is than 500,000. 7 arranged in a uniform metallic casing cup.

There then occur in practice, in the perform- Elimination of the self-excitation otherwise ance of these constructions, the stated interoccurring very, strongly is not performed alone fering oscillations and self-excitations partly in by this combination of the short-circuit con- 40 unusual form, which call for a particular remedy densers 3, i, 5 in groups. -According to the in- 40 forming the subject matter of the present applivention, the cathodes of all single amplifying cation. stages must be connected separately withthe According to the main object of the invention, earthing point 6, each through the medium of a i an mp fi r ar n h s v al p high-frequency earthing condenser 1, whereby tubes for Producing Very high amplification the metallic receiver chassis may be selected as 45 O a frequency'band p t high frequency earthing point, and preferably the connecting fi t s are d in the anodew gridand s point of the condenser I should be in the vicinity d branches of eachv amplifying Stage Containof the appertaining tube base, in which conneci d up condensers connected d t y it tion, however, the connection point should not the cathode of the corresponding be, e ch be situated in the vicinity of parts of the chassis 50 cathode connected directly with the earthing traversed by eddy currents.

point by additional earthing condensers. According to the invention, the supply of the A d s p will now be given, y y Of direct currents from the negative pole of the example only, of an embodiment of the invention, anode-current source is performed through the V reference being made to the drawings wherein medium of chokes 8, and the with over "these 55 chokes must remain the only path of access in respect of the anode current. The natural wave of the chokes 8 is, in accordance with the invention, selected to be smaller than the amplifier Wave lengths in operation, so that the chokes 8, despite the presence of unavoidable parallel building-up capacities, always possess an inductive resistance character. In practice an order of magnitude of .1 mi. has been found to be suificient and very efiective for the condenser I, and 40 windings on a cylinder having a diameter of 20 mm. for the chokes 8. The leads for the grid bias 9 and the anode potential Il] may be disposed as desired, and no longer represent sources of error if the high ohmic series resistance of the grids I l (approximately 50,000 ohms), the anode currents l2 (5,000 ohms) and the screening grids I3, it (each approximately 50,000 ohms) as indicated in Fig. 1 are connected in the manner shown in the invention, 1. e., in such fashion that the same are fully effective as blocking resistances in respect of the high-frequency currents traversing the condensers 3, 4, 5.

With the heating of all stages of the tube from the same heating transformer I, as required in practice, the embodiment of the heating circuit will be as follows:

According to the invention, there are provided between each two branches which conduct the heating current from the two heating lines I 5 and 16 to the single amplifier stages chokes l1, I8 of low ohmic resistance, and in addition the ends of the heating filament for each tube are earthed per se over a pair of earthing blockcondensers i9, 20. This method of heating, earthing and choke feeding in accordance with the invention is of particular importance in practice in the heating circuit of the local oscillator tube, which oscillates in the receiving apparatus to an ultra-short wave. It has been found in practice that if the cart 'ng blocks I9, 20 are not provided for this stage ofthe tube, of if they are not connected in the immediate vicinity of the ends of the heating filament, an exactly defined natural wave is capable of developing in the heating circuit, in view of the frequency of which the reception may be interfered with or rendered impossible by the occurrence of an alien oscillation or an oscillation gap and the like.

According, therefore, to the invention, the pair of condensers I9, ZUand the pair of coils I1, (3 are employed under all circumstances for the heating circuit of the local oscillator tube; on the other hand this method may be adaptedless frequently for the remaining amplifier stages, and in particular may be used for example only after each second amplifier stage (see Fig. 4).

After complete de-coupling of interfering oscillations in the heating circuit circuits of the amplifying tubes there occurred in the practical operation also a third group of interfering oscillations, viz., ultra-frequent selfexcitation of the anode circuits of the amplifying tubes 5, 2, etc. With the choke or transformer amplification over inductances 2|, 22, employed in the case of high-power television receivers there occurs with great certainty upon the combination of amplifying tubes With the stated particularly large steepness, self-excitation on.

an ultra-short wave, the frequency of which is presumably determined by the stray inductance of the anode choke in combination with the anode operating capacity.

In particular the existance of these oscillations can be proved at the anode lead between the tube and in theanode and the anode choke. An oscillation of this nature interferes with normal reception by displacement of the working points, by abnormal anode currents, and by gaps and breaking points and the like when passing over the receiving wave of equal frequency. The existance of oscillations of this character is frequently very diificult to determine. The connection in accordance With the invention of protective resistances 23 in the lead to the anode gap of the amplifying tube has been found to be an efiective remedy. The

resistances 23 should be negligibly small in value comp'ared'with the operating impedances of the anode chokes 2| at the intermediate frequency (approximately 5,000 ohms), but'on the other hand they should have suificient effect on the disturbing frequency oscillation circuit formed by the operating capacity of the tube anode and the stray inductance of the coil, in such fashion that the oscillations are compelled to break off. A 500-ohm resistance which is so constructed as to be free from inductance and low capacity e. g. a normal porcelain and graphite resistance rod, satisfies these requirements without appreciably impairing the receptions.

Fig. 2 shows the manner in which this resistance rod was embodied mechanically, and in what manner the screening means require to be applied so that. the resistance is not bridged by capacities and thus made ineffective. The resistance rod 23 itself is soldered in mechanically rigid fashion to the threaded eye 24. A small tube 25, which is not screened and consists of insulating material, acts as manipulating member and carries at its end the screening sleeve 25', Which is insulated against the anode line 27 for example by means of a rubber tubing 26 and is itself earthed (earth fizreceiver chassis). The screened cable should be as poor in capacity as possible, so that the largest possible ratio C is obtained, and so that with the prescribed carrier frequency as many windings as possible may be Wound on the coupling transformer. In this way there is obtained an amplification increasing in proportion to the square of the windings and proportional to the ratio in the width of the band. 'It is only when observing the de-coupling measures set forth according to the invention and simultaneously employing all of the means described in accordance is coupled in direct fashion with the ultra-short wave aerial.- r

Fig. 3a shows a circuit arrangement of the first valve 30 which is capacity 29 with the cap the head of the valve 30. This capacity 29 is the invention that it is possible to perform up to a total amplification of more for by the connection of the first stage, which formed simply by'a rod inserted in insulated fashion in a sleeve (see the corresponding parts 43 and 38 in Fig. 3) and amounts to 0.1-10- microfarads. The circuit arrangement of the first valve consists of a local-oscillator tube (type tube, whilst all remaining electrodes are passed,

out at the base of the tube .at the bottom. The aerial input connection according to the invention having an oscillation choke 36 and the very small aerial condenser 29 renders the use of a special tuning circuit for the aerial unnecessary. The aerial choke 36 can, however, build up a sufficiently high resistance in an additional frequency range only if the earth capacities in parallel therewith are made as small as possible. According, therefore, to the invention, the choke 36, which is illustrated by way of example in Fig. 3, is constructed as manipulating member. For this purpose it is situated within an insulating tube 31, which carries a jacket sleeve 38 capable of being fitted on the tube cap 39. The screening means, which is required for the lead from the negative pole of a grid bias source of potential, does not commence until after the coil, and is designated 40. The same may be constructed as capacity-loaded rubber cable, and made as long as desired. The sleeve 38, which conducts the bias 4| through the choke 36 to the grid cap 39, is filled out in the interior with insulating material 42, which acts as dielectric for the plug pin 43. The latter is connected with the aerial 28. Inorder now that the lead 44 to the aerial, so far as the same is located within the chassis of the apparatus, will not intercept any oscillations present in the apparatus, for example, the heterodyne oscillations, which would cause self-excitation or radiation, the lead 44 is screened off within apparatus by a screening jacket 45. in accordance with the invention, is selected to be very poor in capacity as compared with the core 44 (diameter ratio 1/10) In this manner a resonance aerial 28 may be utilized for obtaining a potential bulge as large as possible at the point 43.

The measure set forth in Fig. 3 is naturally merely one of several possible constructions solving the problem recognized by the applicant and consisting in making the capacity in parallel with the aerial choke 36 as small as possible and thus making the marginal width ofthe choke as large as possible, at the same time, however, completely screening ofi the aerial circuit 28 against the heterodyne oscillations, and also completely screening off the grid 34 against a directly picking-up of waves in the case of absent aerial.

In Fig. 4 there is shown the special circuit connection of the heating leads in case of a superheterodyne circuit arrangement in which the first stage is an oscillation stage which the following amplifier stages are oscillated to. In the lead line between the heating leads of the first oscillating stage and the associated amplifier stage high frequency chokes l1 and [8 are ar- This screening jacket, however,

earthing condensers,

ranged but between the first and second amplifier stage these chokes between the heating leads are missing and only after the second amplifier stage such chokes are used.

I claim:

1. In an amplifier system with several amplifier stages for obtaining very high amplifications, preferably for amplifying the intermediate frequency band of a television superheterodyne arrangement each of said amplifying stages containing an amplifier tube connected with an anode circuit, a screen grid circuit and a control grid circuit, separate high-frequency filters in said anode-circuit, in said screen-grid-circuit and in said contro-l-grid-circuit of each of said amplifier stages for avoiding disturbing coupling, said filters containing decoupling condensers connected directly with the cathode of the corresponding amplifier tube, each cathode connected directly with the earthing point by additional earthing condensers.

2. In an amplifier system with several amplifier stages for obtaining very high amplifications, preferably for amplifying the intermediate frequency band of a television superheterodyne arrangement each of said amplifying stages containing an amplifier tube connected with an anode circuit, a screen grid circuit and a control grid circuit, separate high-frequency filters in said anode-circuit, in said screen-grid-circuit and in said control-grid-circuit of each of said amplifier stages for avoiding disturbing coupling, said filters containing decoupling condensers connected directly with the cathode of the corresponding amplifier tube, each cathode connected directly with the earthing point by additional earthing condensers, the cathode of each amplifier stage connected with the cathode of the following amplifier stage by a high-frequency choke, the impedance of said choke being purely inductive for the frequency to be amplified and large as compared with the earthing resistanceof said earthing condenser.

3. In an amplifier system with several amplifier stages for obtaining very high amplifications, preferably for amplifying the intermediate frequency band of a television superheterodyne arrangement each of said amplifying stages containing an amplifier tube connected with an anode circuit, a screen grid circuit and a control grid circuit, separate high-frequency filters in said anode-circuit, in said screen-grid-circuit and in said control-grid-circuit of each of said amplifier stages for avoiding disturbing coupling,

said filters containing decoupling condensers connected directly with the cathode of the corresponding amplifier tube, each cathode connected directly with the earthing point by additional the cathode of each amplifier stage connected with the cathode of the following amplifier stage by a high-frequency choke, the impedance of said choke being purely inductive for the frequency to be amplified, and large as compared with the earthing resistance of said earthing condenser, said anode-circuit filters containing additional small ohmic resistance for suppressing ultra-high-frequency oscillations.

4. In an amplifier system with several amplifier stages for obtaining very high amplifications, preferably for amplifying the intermediate frequency band of a television superheterodyne arrangement each of said amplifying stages containing an amplifier tube connected with an anode circuit, a screen grid circuit and a control grid circu1t, separate high-frequency filters in said anode-circuit, in said screen-grid-circuit and in said control-grid-circuit of each of said amplifier stages for avoiding disturbing coupling, said filters containing decoupling condensers connected directly with the cathode of the corresponding amplifier tube, each cathode connected directly with the earthing point by additional earthing condensers, the cathode of each amplifier stage connected with the cathode of the following ,amplifier stage by a high-frequency choke, the impedance of said choke being purely inductive for the frequency to be amplified, and large as compared with the earthing resistance of said earthing condenser, said anode-circuit filters containing additional small ohmic resistance for suppressing ultr.ahigh-frequency oscillations, said small ohmic resistance connected directly With the anode cap, screening means for the anode lead commencing after said insulating tube, said resistance being surrounded by an insulating tube. V

5. In an amplifier system with several amplifier stages for obtaining very high amplifications, preferably for amplifying the intermediate frequency band of a television superheterodyne arrangement each of said amplifying stages containing an amplifier tube connected with an anode circuit, a screen grid circuit and a control grid circuit, separate high-frequency filters in said anode-circuit, in said screen-grid-circuit and in said control-grid-circuit of each of said amplifier stages for avoiding disturbing coupling, said filters containing decoupling condensers connected directly with the cathode of the corresponding amplifier tube, each cathode connected directly with the earthing point by additional earthing condensers, the cathode of each amplifier stage connected with the cathode of the following amplifier stage by a high-frequency choke, the impedance of said choke being purely inductive for the frequency to be amplified and large as compared with the earthing resistance of said earthing condenser, all heating leads of said amplifier stages connected with each other over high-frequency chokes, the impedance of which is purely inductive for the frequency to be amplified and'large as compared with the earth ing resistance of said earthing condenser.

6. In an amplifier system with several amplifier stages for obtaining very high amplifications, preferably for amplifying the intermediate frequency band of a television superheterodyne arrangement each of said amplifying stages containing an amplifier tube connected with an anode circuit, a screen grid circuit and a control grid'circuit, separate high-frequency filters in said anode-circuit, in said screen-grid-circuit and in said control-grid-circuit of each of said amplifier stages, for avoiding disturbing coupling, said filters containing decoupling condensers connected directly with the cathode of the corresponding amplifier tube, each cathode connected directly with the earthing point by additional earthing condensers, the cathode of each amplifier stage connected with the cathode of the following amplifier stage by a high-frequency choke, the impedance of said choke beingpurely inductive for the frequency to be amplified and large as compared with the earthing resistance of said earthing condenser, all heating leads of said amplifier stages connected with each other over high-frequency chokes, the impedance of which is purely inductive for the frequency to be amplified and large as compared with the earthing resistance of said earthing condenser, each of said heating leads associated with the single tubes being connected to earth by a separate earthing condenser.

'7. In an amplifier system with several amplifier stages for obtaining very high amplifications,

preferably for amplifying the intermediate fre-' quency band of a television superheterodyne arrangement including an oscillating stage with associated amplifier stages each of said amplifying stages containing an amplifier tube connected with an anode circuit, a screen grid circuit and a control grid circuit, separate high-frequency filters in said anode-circuit, in said screen-gridcircuit and in said control-grid-circuit of each of said amplifier stages for avoiding disturbing coupling, said filters containing decoupling condensers connected directly with the cathode of the corresponding amplifier tube, each cathode connected directly with the earthing point by additional earthing condensers, the cathode of each amplifier stage connected with the cathode of the following amplifier stage by a high-frequency choke, the impedance of said choke being 7 purely inductive for the frequency to be amplified and large ascompared with the earthing resistance of said earthing'condenser, the heating leads of the oscillating stage being connected with the heating leads of the following amplifier stage byhigh-frequency chokes, the heating leads of the associated amplifier stages being also connected with each other by high-frequency chokes but so that only between each second amplifier stage high frequency chokes are arranged, said chokes being purely inductive for the frequency to be amplified and large as compared with the earthing resistance of said earthing condenser;

KURT SCI-ILESINGER. 

